1. Field
One or more embodiments relate to an electrode-current collector sheet for capacitive deionization, a capacitive deionization device and an electric double layer capacitor having the same.
2. Description of the Related Art
Capacitive deionization (“CDI”) is a technique for removing an ionic material from a medium by absorbing the ionic material into a surface of a carbon electrode having nano-sized pores by applying a first voltage to the carbon electrode. To regenerate the carbon electrode, a second voltage opposite in polarity to the first voltage is applied to the carbon electrode so as to remove the absorbed ionic material, and the ionic material is discharged with water. CDI may operate without chemicals to regenerate the carbon electrode, and may operate without an ion exchange resin, a filter or a membrane. Also, CDI may improve capacitance of the medium without discharging hardness components, such as Ca2+ or Mg2+, or harmful ions, such as Cl−.
In CDI, when a direct current (“DC”) voltage having a low potential difference versus the medium is applied to a carbon electrode while a medium, i.e., an electrolyte containing dissolved ions, flows through a flow path and contacts the carbon electrode, anions are absorbed and concentrated at an anode and cations are absorbed and concentrated at a cathode. Accordingly, when application of the DC voltage is stopped, the concentrated anions and cations are desorbed from the anode and cathode, each of which may be a carbon electrode.
The carbon electrode desirably has a low electrical resistance and a large specific surface area, and thus the carbon electrode is manufactured by binding an activated carbon with polytetrafluoroethlyene (“PTFE”), or the carbon electrode is manufactured by carbonizing a resorcinol formaldehyde resin and then performing a complicated drying process, thereby obtaining a carbon electrode having a plate-like shape.
Electrode sheets, which are formed in a sheet shape by binding an activated carbon with PTFE, are used in commercially available CDI electrodes. Cells for CDI devices are manufactured by pressing together the electrode sheets and the current collectors, which can be a graphite foil. Graphite foils have corrosion stability in charge/discharge regions of CDI devices, unlike metal current collectors. However, in cells manufactured as above, since an electrode sheet and a current collector are separately formed, a contact area between the electrode sheet and the current collector decreases, thereby increasing an electric resistance. Also, it is desirable to reduce pressure loss in CDI. It is therefore desirable to have an electrode-current collector sheet that provides reduced electrical resistance between an electrode sheet and a current collector. It is also desirable to have a cell for CDI having reduced pressure loss in an electrolyte flow path.